Reinforcement of Old Precast Slab Houses

The reinforcement of old precast slab houses requires selecting scientific solutions based on the type of floor slab, the extent of damage, and the intended use. Common methods are as follows:

I. Floor Slab Load-Bearing Capacity Reinforcement

1. Carbon Fiber Sheet Adhesion to the Bottom of the Slab Suitable for residential or office buildings with minimal load increase, fine cracks (width < 0.3mm), and sensitivity to ceiling height. By adhering carbon fiber sheets to the bottom of hollow slabs with structural adhesive, the load-bearing capacity can be enhanced, and crack propagation can be restricted. This method features a short construction period and minimal disturbance to the original structure.

2. Steel Plate Adhesion to the Bottom of the Slab Adhere 3-6mm thick steel plates to the bottom of the slab, utilizing the high elastic modulus of the steel to significantly improve slab stiffness and reduce vibration and deflection. This method is suitable for locations with high performance requirements (such as libraries and computer rooms), but attention must be paid to the anti-corrosion treatment of the steel plates.

3. Installation of Steel Beam Supports Install H-shaped or I-shaped steel beams (cross-section ≥ 200*200mm) beneath the slab using chemical anchors or rebar planting, with the steel beams bearing the primary load. This method causes minimal disturbance to the original structure and is particularly suitable for renovated houses or areas with localized heavy loads (such as kitchens and balconies). The renovation project of an old house in Zhongxing Town, Chongming, adopted this method.

4. Overlay Layer Reinforcement on the Slab Surface After chiseling off the original slab surface leveling layer, lay a two-way steel mesh and pour 40-80mm thick high-strength fine aggregate concrete or polymer mortar. This method can simultaneously enhance load-bearing capacity, stiffness, and waterproofing performance, but it will reduce indoor ceiling height. The impact of the added self-weight on the lower structure must be evaluated.

II. Crack and Local Damage Repair

1. Crack Repair For non-structural cracks (width < 0.3mm), use epoxy resin pressure grouting for closure; structural cracks require treatment in conjunction with load-bearing capacity reinforcement solutions.

2. Local Strengthening For areas with concrete spalling or exposed rebar, first remove rust and apply rust inhibitors, then restore the cross-section with high-strength repair mortar. This is an auxiliary measure often used in conjunction with other reinforcement methods.

III. Enhancement of Integrity and Seismic Resistance

1. Slab Joint Treatment Chisel grooves at slab joints, implant tie bars, and pour fine aggregate concrete to form a 'post-pour strip,' enhancing the connection between slabs.

2. Slab End Reinforcement Add angle steel or concrete edge beams to prevent slippage and脱落 (tuōluò, detachment), improving the seismic performance of the joints.

3. Monolithic Pouring Layer on the Slab Surface Uniformly lay a steel mesh fine aggregate concrete monolithic pouring layer to connect the individual precast slabs into a whole, significantly improving the overall structural integrity.

IV. Reinforcement Precautions

1. Structural Safety Assessment Before renovation, comprehensively inspect the width of cracks in the precast slabs (special treatment required for widths > 0.3mm) and the connection status with the ring beams (replacement required if bolt corrosion rate > 30%).

2. Temporary Support System During construction, install steel pipe supports every 1.2 meters along the length of the precast slab to prevent collapse risks.

3. Construction Sequence Control Follow the principle of 'middle first, then sides,' with a daily removal amount not exceeding 30% of the total floor slab area. Continuously monitor changes in support stress and prohibit heavy hammer impact removal.